A multidisciplinary study of renal disease in children and experimental rat models includes a number of approaches. The control of C3 biosynthesis is being examined in human monocytes. The C3 nephritic factor has been identified as an immunoglobulin, a specific antibody to C3bBb. Its idiotypic determinants are being investigated. C1 biosynthesis by normal and malignant transitional epithelium is under study as a potentially useful marker of renal tract malignancy. The ultrastructural lesion of autologous immune complex nephritis is being compared in Munich-Wistar rats and Lewis rats. The composition of cryoglobulins in acute post-streptococcal glomerulonephritis reveals the presence of almost exclusively IgG in comparison with SLE cryoglobulins. Comparison of hyporesponder strains (DFA/2 rats) with normal responders (Lewis rats) to proximal tubular antigen reveals genetic control of variant suppressor function. Chemical modification of the antigen overcomes suppressor differences.